Vegetation Monitoring in Nelson

Monitoring vegetation helps Council understand the health and structure of native ecosystems, track changes over time, and assess the impacts of pests such as browsing animals.

Since 2013, Nelson City Council has been monitoring vegetation across key conservation areas, including the Maitai, Brook, and Roding Reserves.

Why We Monitor Vegetation

These reserves contain significant natural values, including:

globally unique biodiversity and important habitats
ecosystems that store carbon and reduce flooding and erosion
drinking water catchments for Nelson
important cultural sites and recreational areas

Vegetation varies across these reserves due to differences in soils, including specialised plant communities on ultramafic and limestone soils.

Monitoring helps identify:

where vegetation is healthy or under pressure
which species are regenerating
where management action is needed

The Impact of Deer and Goats

Introduced browsing animals such as deer and goats (ungulates) are a major pressure on native vegetation.

New Zealand plants evolved without mammalian browsers, so many species lack defences and are highly vulnerable.

Ungulates:

selectively eat the most palatable plants
prevent seedlings from establishing
gradually change forest composition

Over time, this can lead to:

loss of palatable native species
bare or simplified forest understorey
dominance of less palatable plants
long‑term changes to ecosystem structure

Even low numbers of deer or goats can cause significant damage.

How We Monitor Vegetation

Council uses a method called the Seedling Ratio Index (SRI), developed by Manaaki Whenua – Landcare Research.

This measures the balance between:

plant species that animals prefer to eat
those they avoid

Survey method

Monitoring is carried out along transects across different vegetation types
Each transect is 400 metres long with 20 survey points
At each point, seedlings are counted and recorded:
- Short seedlings (under 30 cm)
- Tall seedlings (30 cm to 2 m)

Plants are grouped into categories based on how likely they are to be eaten:

preferred
not selected
avoided

This allows Council to track regeneration and browsing pressure over time.

What We’re Seeing

Monitoring results from 2013 to 2023 show that browsing by deer and goats is having a significant impact on native vegetation in Nelson’s conservation reserves.

Palatable plant species are not regenerating as expected, with consistently low seedling numbers
Forest understorey composition is shifting toward less palatable species
Browsing pressure has increased over time, with animals now feeding on species they previously avoided
Regeneration rates have slowed across multiple plant groups

These changes affect not just individual species, but the structure and long‑term health of forest ecosystems.

What We’re Doing

Council is responding through monitoring, pest management, and long‑term planning:

managing deer and goat numbers through recreational and contracted hunting
using vegetation monitoring to assess ecosystem health and guide decisions
targeting pest control in areas of high ecological value
managing other threats such as possums, pigs, predators, and pest plants
continuing long‑term monitoring to track changes over time
exploring options to protect vulnerable areas, including fenced exclosures

Monitoring shows that protecting sensitive vegetation will require very low levels of browsing animals, particularly in fragile ecosystems.

Sites such as the Brook Waimārama Sanctuary, where browsing animals are excluded, demonstrate the potential for significant regeneration when pressure is removed.

What You Can Do

You can help protect native vegetation in Nelson by:

supporting or participating in pest control and restoration projects
managing browsing animals where appropriate
protecting and planting native species on your property
controlling pest plants such as old man’s beard and wilding conifers
avoiding damage to fragile vegetation areas

Community effort plays an important role in protecting Nelson’s biodiversity.

Check out all the ways you can get involved in protecting our nature - What You Can Do